Known in the art is a flexible pipe whose design makes it possible to transmit working media under increased pressure and at the same time to receive an axial tensile force (French Pat. No. 2,142,764). Said flexible pipe comprises a rubber supporting pipe onto which pipe several layers of metal braid are wound in spiral. The lowest layer and the uppermost layer are wound with a shift in the winding angles of from 6.degree. to 80.degree.. Metal wires in all the layers are subject to tension and allow the flexible pipe cross-section to be preserved at a slight bending thereof under conditions of simultaneous influence of gage internal pressure and a slight axial tensile force.
However, such a flexible pipe cannot be applied in the case of effect of distributed or local external load, e.g. under the influence of gage external pressure. Under the effect of compression in the radial direction, the cross-section of the flexible pipe loses its stability due to the fact that the metal wires constituting the braid cannot resist this effect.
Also known in the art is a flexible pipe which is intended to receive, without deformation, apart from gage internal pressure and an axial tensile force, gage external pressure (USSR Inventor's Certificate No. 668,625). In accordance with the above disclosure, this flexible pipe comprises an inner supporting pipe constructed from an elastic material onto which pipe a flat strip from a rigid material (e.g. metal) is wound. The above strip forms a cylindrical power casing with an interlayer from an elastic material being put thereupon. Two layers of shaped rods are wound in crossed directions onto said interlayer. The cross-section of each rod has a maximum size in the radial direction. Said rods are wound symmetrically at angles of up to 40.degree..
Undoubtedly, the presence of the rods wound at such angles will allow the flexible pipe to receive an axial tensile force and gage internal pressure without fracture. However, if such a flexible pipe is placed into a medium whose pressure exceeds the pressure within the flexible pipe, the deformation of the flexible pipe becomes possible even at the pressure drop of 4 to 5 kg/cm.sup.2, said deformation being accompanied by the loss in stability of its cross-section. This is due to the fact that the pressure of the external medium is freely transmitted through the gaps between the shaped rods (especially under tension) to the interlayer made from an elastic material and, correspondingly, to the power frame formed by the flat strip. The rigidity of this frame in the radial direction is low and is in no way reinforced by the shaped rods which are by themselves subject only to tension. Thus, the power frame, after having lost its stability, will be locally pressed into the flexible pipe. Simultaneously, the turns of the flat strip will separate, and the tightness of the flexible pipe will be certainly upset. Naturally, the above shortcomings will take place only at differentials in internal and external pressure of more than 4 to 5 kg/cm.sup.2.
To our opinion, the most successful is a construction of a flexible pipe developed by the company "Coflexip S.A." (see advertising brochure "Coflexip flexible pipe for the offshore industry" by this company, published in 1979). The above flexible pipe comprises an inner supporting pipe constructed from an elastic material, a shaped strip having a Z-shaped cross-section and wound in a spiral onto said pipe. The Z-shaped cross-section of the strip is formed by two stepwise conjugated parallel flanges. The upper and the lower flanges are conjugated therebetween by means of a leg. Each flange is constructed in the form of an angle and rests by the edge of this angle on the opposite flange of the next turn of the strip. Thickness of each flange is substantially less (5 to 10 times) than the height of the strip profile. The above design is substantially one of modifications of the invention of a S-shaped profile. Thus, said angles of adjacent turns of a strip are put into engagement and limit the possibility of extending the power frame formed by the strip, in the axial direction. An interlayer of an elastic material is superimposed onto the power frame formed by a shaped strip. On the interlayer, there is provided at least one pair of reinforcing layers formed by groups of power filaments, said groups being parallel to one another, and wound substantially in a symmetrical position. The power filaments are provided in the form of steel wires and are wound at angles of 40.degree. to 60.degree. to the axis of the flexible pipe. The flexible pipe is also provided with an external protective shell made from an elastic material.
An obvious advantage of the above described construction of the flexible pipe consists in that such a design makes it possible to receive three types of loads: an axial tensile force, gage internal pressure, and gage external pressure. A sufficiently good perception of the gage external pressure is promoted by the fact that the strip forming the power frame is made in the shaped form, and all the structure of the flexible pipe is hermetically sealed by the external protective shell. While possessing the above advantages, the flexible pipe can maintain its flexibility.
Nevertheless, in the manufacture of such a flexible pipe it is necessary to utilize such expensive and high quality materials as alloy steels, titanium etc. Such a need is caused by the following considerations: a comparatively small thickness of flanges is required to provide for reliable engagement between the angles thereof because with the above mentioned angles of winding the power filaments, the latter do not ensure the complete perception of the total axial tensile force. Therefore, to avoid distortion of uniformity of the power frame (i.e. to eliminate the possibility of formation of through gaps between the strip turns under tension), the presence of engaging angles is necessary. For this reason, and also due to a rather complex technology of strip shaping, reinforcement of said strip by increasing the thickness of the flanges is impracticable. Moreover, the upper flange of each turn of the strip rests on the lower flange of the adjacent turn with a comparatively narrow edge of the angle. Consequently, the material from which the shaped strip is constructed, must possess high physico-mechanical properties, including high hardness among them. It will be understood that in order to reinforce the power frame, the power filaments of the reinforcing layers are also to be constructed from a high-strength steel wire. It should be also noted that the strength of the power frame receiving a portion of the axial tensile force is determined essentially by the strength of the weakest joint between two adjacent turns of the strip. The above consideration imposes especially high demands upon the production process of the shaped strip and the frame.
Disclosure of the Invention
The principal object of the present invention is to provide a hose in which the structure of reinforcing layers and the construction of a frame allow inexpensive materials to be used for the manufacture of the same hose without reducing its strength. The object set forth is attained by that in the flexible pipe comprising an inner supporting pipe made from an elastic material; a power frame formed by a shaped strip having a Z-shaped cross-section with two stepwise conjugated flanges, the strip being wound in a spiral fashion onto the supporting pipe in such a way that the upper flange of each turn is disposed over the lower flange of the adjacent turn, an interlayer made from an elastic material and superimposed onto the power frame, at least one pair of reinforcing layers formed by groups of power filaments, said filaments being parallel to one another and wound in contrary onto said interlayer; and an external protective shell made from an elastic material, according to the invention, each of said flanges is of a quadrangular cross-section and is of a height equal to one half of the height of the profile of the strip so that the upper flange of each turn rests directly on the lower flange of the adjacent turn, and the ends of the upper flanges as well as the ends of the lower flanges are aligned, the power filaments of each reinforcing layer being wound at angles of from 0.degree. to 20.degree. to the axis of the pipe.
It turned out that with such a construction of the flexible pipe all the axial tensile force is received by the power filaments constituting the reinforcing layers. Therefore, there is no need in any angles engaging the turns of the shaped strip and limiting mutual displacement of these turns in the axial direction. Thus, elimination of the effect of the axial tensile load upon the power frame made it possible to get rid of the most vulnerable link represented by the angles engaging the turns of the strip therebetween. This has resulted in a considerable simplification of the production process of the shaped strip and has provided for a possibility of manufacturing said strip from such inexpensive materials as low-carbon structural and tool steels. Consequently, there are no conditions for the local wear of the strip as it took place in the prior art construction. The same factor makes it possible to substantially lower such a requirement placed upon the material as hardness thereof. Combination of the above characteristics makes it possible to increase durability and reliability of the flexible pipe, and to considerably lower its cost.
In the construction of a flexible pipe intended for operation under conditions of constant effect of the dynamic axial tensile load, the interlayer from an elastic material is expedient to have a helical expansion disposed above the butt formed between the ends of the upper flanges of the strip turns.
With sudden application of the axial tensile force, the supporting pipe and the interlayer are deformed first, the helical expansion is straightened out, and only then the power filaments get strained and come into operation.
For operation at very large depths, such a modification of the flexible pipe is advisable wherein between the power frame and the lower reinforcing layer of the power filaments wound at angles of 0.degree. to 20.degree., there is provided at least one layer of a similar shaped strip wound in the opposite direction.
A modification of the flexible pipe is preferred, wherein between the interlayer from an elastic material and a pair of reinforcing layers of the power filaments wound at angles of 0.degree. to 20.degree., there is provided a layer formed by the power filaments wound at an angle of 30.degree. to 60.degree. to the axis of the flexible pipe.
It turned out that with such a construction the flexible pipe can receive a torque and an axial compression force. Rigidity of the flexible pipe is proportional to the magnitude of the torque. Power filaments wound at an angle of 30.degree. to 60.degree. increase their angle of winding under the effect of such loads and squeeze the power frame while shifting the turns of the strip and thereby making said frame rigid and strong.
To ensure joint operation of all the layers and to eliminate the possibility of wearing-through the power filaments, it is expedient that the layer formed by said power filaments wound at an angle of 30.degree. to 60.degree. be closed by an additional interlayer from an elastic material.
The widest performance possibilities has a modification of the flexible pipe wherein on the ends of the flanges of the shaped strip there are provided longitudinal projections and grooves being congruent thereto, into which grooves said projections enter when the turns of the strip are brought together. Such a flexible pipe possesses flexibility both in unloaded state and under the effect of an axial tensile load. However, under the effect either of an axial compression force, or of a torque, the flexible pipe is transformed into a rigid pipe. The projections and the grooves provided at the ends of the flanges, ensure reliable engagement between the turns.
It is expedient that the flanges forming the profile of the strip cross-section, have a form of parallelograms. In this case the ends of the flanges in the strip turns have a conical shape, thereby ensuring self-alignment of the turns being brought together.
The same effect is achieved in a modification of the flexible pipe wherein the ends of the flanges having the cross-section in the form of a parallelogram, are rounded and have similar curvature radii. Roundings of the ends impart the flexible pipe an increased flexibility in the unloaded state.
The object set forth is also attained by that there is provided a method for manufacturing a flexible pipe, comprising the steps of superimposing a shaped strip preliminarily bent in a spiral, onto an inner supporting pipe, covering the power frame formed by the shaped strip, with an interlayer from an elastic material with simultaneous fastening said interlayer to the strip; winding reinforcing layers, and superimposing an external protective shell, wherein, according to the invention, prior to covering the power frame with the interlayer, the internal supporting pipe is fixed to the shaped strip, stretched along the axis thereof, and after superimposing the external protective shell is released from the action of the axial tensile load.
This makes it possible to wind reinforcing layers onto a smooth cylindrical surface of a blank of the interlayer, while the spiral expansion on said interlayer is formed after releasing the supporting pipe the axial tensile force.
It should be noted that the supporting pipe is returned into the initial state without formation of any crimps or wrinkles on the surface thereof.